Pokémon Chaos Black is a third party version of Pokémon FireRed that was released on the Game Boy Advance and as a ROM. The game features a slightly modified map, some new graphics, 60+ new Pokémon and a tweaked storyline. The game was produced to fill the void left by the lack of a special edition version of FireRed and LeafGreen (e.g. Ruby/Sapphire/Emerald,Diamond/Pearl/Platinum.).
The game was developed by 'MewThree Inc.' and was released online in 2004 and on GameBoy Advance in 2005. When playing the game, the chance of a Shiny Pokemon appearing are 100-1 which is considerably less than FireRed's 8,000-1. The game also features new Legendary Pokémon such as MewThree, MewThree X and MewTrance. The Pokemon on the box and menu screen was inspired/modeled on a character from the Sonic The Hedgehog series called "Chaos", who appears in Sonic Battle, Sonic Adventure 2 and several other games. Although in the game Chaos is unobtainable, it still serves as the game's mascot.
The game's legality is a big issue - it was created as a non-profit fan-game, but is still considered an illegal product as is it not licensed by Nintendo. Nintendo has taken no legal action against the developers, 'MewThreeInc'. However, Chaos Black is not made any more and, in turn, has become more of a collectors' item.